1. Field of the Invention
The present invention relates to an image processing apparatus and method for performing a color process according to an ambient light in case of observing an image.
2. Related Background Art
Color image products have recently been diffused popularly, and thus a color image can easily be managed not only in a specialized field such as, e.g., design formation using a computer graphics (CG), but also in a general office, whereby a number of input and output devices have widely been used. Therefore, a serious problem has occurred relating to a difference in color becomes due to the use of different devices, suggesting the need for a color management system for solving such a problem.
The color management system eliminates the difference in color among respective devices by using the common color space. The system is based on a concept that, if the color is positioned at the same coordinates in one color space even in the different device, such color can be viewed as the same color. On the basis of this concept, in the system, all of the colors are represented by using the single color space, which acts as a reference color space, so as to make the color at the same coordinates seem coincident. At present, it is proposed, as the color space, a method that XYZ three stimulus values (or tristimulus values) be used to correct the difference in color for each device.
However, in a case where a light-emission color (light source color) which is displayed on a monitor coincides with a color (material color) of such as a printed matter which can be seen by means of light reflection, the difference in color cannot fully be corrected only in the above manner due to a difference in color mode.
For example, in a case such as where an image read by a scanner is displayed on a monitor or the image displayed on the monitor is printed, an observation is frequently performed with a juxtaposing between the monitor and the printed matter or original. In this case, there is a problem that the color on the monitor is different from the color on the printed matter or original.
In such a case, the image on the monitor or the original is not always observed with a determined ambient light. That is, a kind or brightness of a light source is being varied. Therefore, if the color on the monitor is desired to be the same as the color on the original, it is necessary to obtain information concerning such observation environment (i.e., ambient light information). Then, in case of performing the observation in one environment, it is predicted based on the ambient light information obtained by a sensor what value (e.g., an XYZ value) the image obtains, to reproduce the obtained value as faithfully as possible by using a profile for each device, thereby making the seem coincident the color at the same coordinates coincident (color-measurement or colorimetry coincidence).
However, the environment where the actually-output image is observed is not always equal to the environment where an image output apparatus is placed. That is, in general, both the image output by a printer and the image copied by a copy machine are observed in various environments. In the above-conventional apparatus, since an ambient light sensor is built in the image output apparatus, if the image is observed in the environment where the image output apparatus is being placed, the color correction can fully be performed taking the environment into consideration. However, if the image is observed in an environment (e.g., other conference room, branch office or the like) which is different from the environment where the image output apparatus is being placed, the image which is optimized taking its observation environment into consideration cannot be output. Therefore, a phenomenon occurs that the color of the image which is actually seen by a user does not seem to coincide with the color of the image at the time when such image was formed.
Further, it is supposed that the ambient light sensor is mounted on various places, e.g., a front surface of the monitor, an upper portion of the printer, a front desk of the printer and the like. Therefore, the ambient light to be detected varies according to the place on which the ambient light sensor is mounted.
Furthermore, since the monitor is an emitter or an illuminant, if the monitored image is observed always in the same ambient light, the color does not seem to remarkably vary even in different observation states. On the other hand, if the printed image is observed, even if such the observation is always performed in the same ambient light, a light quantity which enters into observer's eyes varies in accordance with the observation states. For example, in a case where the printed image is observed under a ceiling light of an office or the like, if it is supposed that the printed image is compared with the monitored image with inclining, standing and placing on an original stand the printed image, the light quantity entering into the observer's eyes varies according to each observation state even though the same image is being observed in the same ambient light.
However, the position at which the ambient light sensor is mounted is conventionally determined in relation to hardware. Therefore, in order to calculate by using information obtained from the sensor the light quantity which is actually sensed by the observer, one observation state of the image has previously been determined, and then data obtained from the sensor is converted into the light quantity which is actually sensed by the observer by using the two determined information.
In such a conventional method, if the actually-observed state is the same as the previously-determined state, no problem will occur. However, such a same state cannot always be obtained.
For example, in a case where it has been supposed the image observation environment is that the printed image is observed with a 45.degree. incline from a table and a data conversion method has previously been determined based on such supposition, even if the observer actually observes the printed image standing vertically, merely the information in case of inclining the printed image by 45.degree. can be obtained as ambient light data in the conventional method. Therefore, since the actual observation environment is different from the observation environment at the time of determining the conversion method, the colors obtained in these two environments cannot be seen as the same color.
Similarly, in a case where mounting position and direction of the ambient light sensor can be changed, actually-measured ambient data differs in accordance with the position and direction of the ambient light sensor. For example, in the case where the printed image is observed under the ceiling light, measured data varies depending upon whether the sensor is positioned on the ceiling light vertically or positioned horizontally. Therefore, if an ambient light calculation method is not determined based on both the position and direction of the sensor with respect to the light source and the image observation environment, the ambient light suitable for actual observation state cannot be obtained. As a result, the image on the monitor and the printed image cannot be seen as a same-color image.
The above problem occurs also in a case of outputting the image by a printer, irrespective of the difference between the light source color and the material color. That is, in a case where a color process is performed in the printer by using information from the ambient light sensor, one of the observation states of the output image is determined as a standard observation condition, and then the information from the sensor is converted such that the ambient light sensed by the sensor becomes an ambient light which should be sensed by a human when he observes it in the standard observation condition. However, when the observation state is actually different from the previously-determined condition, as in the above cases, the ambient light information which is actually sensed by the observer becomes different from the ambient light information which has been converted based on the standard observation condition.